Humans are affecting oceans all around the world – through fishing, pollution and climate change. Overfishing has become a particularly burning issue over the past few decades, as many commercially exploited fish stocks have declined to historically low levels.
In addition, a new problem seems to be emerging – fish around the world are getting smaller. One reason for this decrease in size is the fishing itself, as large, usually older fish are being caught and only young and small fish are left.
However, it goes deeper than that. If we take a fish today and compare it with a fish of the same age from the past, the fish of today are often smaller than they used to be a century ago. And again, it is fishing that appears to be the main culprit.
Fishing is typically size-selective, and it is usually the largest individuals that are being targeted. Rules around mesh sizes and minimum landing sizes mean that the largest fish are caught and kept. These regulations aim to protect young fish and allow them to grow and reproduce at least once before they are caught.
While the intent seems logical, there are unintended consequences of this policy. Fishing in this way may drive evolution towards smaller body size and earlier reproduction. The situation is equivalent to animal breeding except that it works in reverse – animal breeders leave the most...
